To provide a combined power generating system for making resources for solar energy (thermal energy) accumulated in every materials (heat sources) on the earth as electricity and the thermal energy which are effective for humans.

A process A for vaporizing compressed gas heating medium, vaporized at a temperature or lower of a material heat source by being brought into contact with the heat source through a heat exchanger, a process B for adiabatic expansion of the vaporized heat medium, and a process C for radiating heat, compressing and liquefying a heating object by adiabatically compressing expanded gas or gas-liquid mixture and by heating the heating object by the other heat exchanger than the heat exchanger, are circulated connectedly. Exergy change of the processes A, B, C is taken out as electric energy, and cold heat of a low-temperature heat medium of the process B and hot heat of the process C are utilized as an effective energy source. The combined power generating system and a low-temperature steam power generating system by a Kalina cycle using a nonazeotropic heat medium or its improved cycle are connected to each other, and hot heat energy generated in the process C in the system is set as the heat source of the system.